Finding the Fourth Proportional to 139.56, 209.34 and 85.88

Step by Step Solution

1. Step 1: Write the proportion equation
   139.56 : 209.34 = 85.88 : x
2. Step 2: Convert to fraction form
   139.56/209.34 = 85.88/x
3. Step 3: Cross multiply
   139.56x = 209.34 × 85.88
4. Step 4: Simplify right side
   139.56x = 17,978.12
5. Step 5: Solve for x
   x = 17,978.12/139.56
6. Step 6: Final answer
   x = 128.82